Patent Application
20100229811
This application claims the benefit of German Patent Application No. 102009012927.8, filed Mar. 12, 2009, which is incorporated herein by reference as if fully set forth.
The invention relates to a switchable component advantageously constructed as a tappet or support element in a valve train of an internal combustion engine, with a housing in whose borehole an inner element is held so that it can telescope, wherein at least one coupling piston guided by an anti-rotation locking device sits in a radial borehole of the inner element in a decoupled case, with a section that is flattened in some areas being inherent in this coupling piston on one axial side starting from its outer end, wherein the borehole of the housing has a window or an annular groove/an annular-groove segment with a complementary engagement surface against which, in a coupled case, the coupling piston can be displaced with its flattened section when passing through the cam base circle and wherein an edge between the outer end and the flattened section of the coupling piston is provided with a bevel.
DE 10 2005 020 580 A1 discloses a switchable component constructed as a roller tappet whose coupling piston is bulged cylindrically in the section of an edge between its outer end and flattened section. An anti-rotation locking device for the coupling piston is created by the annular element emerging from FIG. 2 of the document noted above, with this annular element lying underneath the flattened section of the coupling piston and being guided on the outer shell of the inner element. The measure named above should avoid a two-point contact in the case of unavoidable tilting of the coupling piston on its engagement surface in the housing. The coupling region in the prior art named above, however, must have fine tolerances, which is extremely complicated, in order to always guarantee that, for coupling, an upper edge of the annular element is slightly higher as shown than the opposite engagement surface of the housing of the coupling piston when passing through the cam base circle and internal stop position of the inner element. In this way, even for a maximum, undesired twisting of the coupling piston, its secure, unimpaired travel into the coupled position is guaranteed and at the same time it is prevented that this impacts with an edge section of its edge on the engagement surface of the housing.
A goal of reducing the manufacturing costs in mass production, however, necessarily also leads to the tolerances becoming less fine or to the selection of manufacturing processes that are associated with a greater deviation from the desired dimensions of the components. In the case of a switchable component according to DE 10 2005 020 580 A1, for the most unfavorable tolerance position, this has the result that, in a stop position of the inner element (passing through the cam base circle), an upper edge of its annular element is lower than the engagement surface of the housing and the coupling piston twisted to a maximum in its holder of the inner element forms a spring-force-loaded contact with an edge region on the inner edge of the engagement surface, without reaching its coupled position. The latter state leads at least to undesired wear of the coupling piston and also the inner edge of the engagement surface.
In addition, U.S. Pat. No. 6,578,535 B2 is also referenced. This document discloses, in FIG. 5, a coupling piston whose edge is provided with a planar bevel.
The objective of the invention is therefore to create a switchable component of the type noted above in which the cited disadvantages are eliminated. In particular, a component should be created whose coupling piston couples in a reliable and low-wear way even for the most unfavorable tolerance situation.
According to the invention, this objective is met in that the bevel is provided as a surface section of an ellipsoid whose longitudinal axis runs parallel to the flattened section.
In this way, the disadvantages described above are eliminated. Due to the elliptical or spherical surface of the bevel with “drawn-in” edge regions, the coupling piston then also “slips” on the engagement surface on the opposite housing, when this is rotated at a maximum and even with its edge region lying under the inner edge of the engagement surface. The wear described above no longer must be taken into account. At the same time, it is obvious that, due to the arc-shaped, curved bevel on the coupling piston, the latter is supported with a wide contact surface directly at the beginning of the coupling.
In the case of a construction of the engagement surface of the housing in an annular groove or an annular-groove segment, the profile of the bevel should be adapted to the radius of a base of the annular groove or the annular-groove segment, so that here an edge contact is avoided.
One special advantage of the invention is also to be seen in that the available contact surface of the flattened section is not minimized for the coupling.
Due to the measures according to the invention, at least the coupling region of the switchable component can have larger tolerances, which ultimately represents a contribution in the direction toward lowering the manufacturing costs.
According to one preferred refinement of the invention, the flattened section of the coupling piston runs to a point starting from its edge in the direction toward its inner end at a small angle on another axial side of the coupling piston. Due to this slight “rearward” angular offset of the flattened section it is guaranteed that a contact zone lies outside of the inner edge region of the engagement surface during the coupling.
Additional constructions relate to preferred possible embodiments of the anti-rotation locking device for the coupling piston. According to a first preferred variant, there is the annular element already mentioned above on which the coupling piston lies with its flattened section. Alternatively, it is also conceivable and provided to allow a pin to project into the radial borehole of the inner element, wherein this pin is engaged with a corresponding longitudinal groove on the outer shell of the coupling piston.
The measures according to the invention are indeed also conceivable in a switchable component in which only one coupling piston is provided. With respect to surface pressure and tipping, however, it is more advantageous if two diametrically opposed coupling pistons are provided in the inner element. If necessary, even more than two coupling pistons distributed equally around the periphery could be applied. The radial borehole for the coupling piston could be constructed here as a through hole or blind hole.
As the switchable component, a roller, sliding, or cup tappet or a support element for a rocker arm are possibilities. It is also conceivable and provided, however, to perform the measures according to the invention in a switchable rocker-arm system.
The invention is explained in detail with reference to the drawing. Shown are:
The inner element 4 has, in a lower section, a radial borehole 5. In this lie two compression-spring-loaded coupling pistons 7 facing diametrically opposite each other. A coupled position of the coupling pistons 7 is shown in
For the coupling, on the radial outside, a window 11 in the housing 2 with a lower engagement surface 12 lies opposite the coupling piston 7. For presenting the coupling, when passing through the cam base circle, the inner element 4 contacts stop 18 (here, securing ring assembly) arranged in the borehole 3 of the housing 2. The axial extending movement of the inner element 4 relative to the housing 2 is generated by the force of lost-motion spring 17 constructed as a compression spring assembly.
As
As
For particularly unfavorable tolerance fields, if the coupling piston 7 is rotated at a maximum and is at a low position directly before coupling, so that its bevel 14 lies lower with an edge area 19 than an inner edge 20 of the engagement surface 12 of the window 11, the coupling piston 7 reaches its coupled position, despite everything, due to its bevel 14 constructed as a surface of an ellipsoid, in that, stated simply, it “slips” or “rotates in” on the engagement surface 12 of the window 11. Blocking of the coupling movement of the coupling piston 7 or at least wear in the edge region are thereby avoided.
If necessary, at least the sections of the coupling piston 7 engaged with each other and the window 11 can be provided with suitable anti-wear measures, such as, heat treatments and/or deposited coatings.
Overall, due to the ability to make the tolerances larger at least in the coupling area of the component 1, it is possible to reduce the manufacturing costs.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102009012927.8 | Mar 2009 | DE | national |
